A label-free G-quadruplex and ThT mediated fluorescent sensor for detection of Cu2+ from water samples

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A facile and label-free detection method based on the formation of the G-quadruplex structure of Thioflavin T and a DNA sequence was developed for rapid and sensitive detection of copper (Cu2+) ion. The DNA sequence with many guanine (G) repeats has the potential to form a G-quadruplex structure and exhibits high selectivity to Cu2+. ThT promotes the formation of the G-quadruplex structure resulting in high fluorescence intensity because of its fluorescence molecular rotor characteristic. As opposed to, when the DNA sequence binds to its target in the presence of Cu2+, conformational changes occur, resulting in ThT dissociation and a substantial decrease in fluorescence intensity. By virtue of this change, unlabeled, low-cost, sensitive, and selective detection of Cu2+ was achieved and not interfered by many other ions. The proposed method has high sensitivity and selectivity, with a detection limit of 30.7 nM, allowing it to directly measure Cu2+ in contaminated water samples in a wide linear range from 0.1 to 100 µM with a high recovery rate.